Content-type: text/html Manpage of wsrtuvmodel


Section: User Commands (1)
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wsrtuvmodel - Add, subtract, etc, a model from a uv data set.  




uv analysis  


WSRTUVMODEL is a MIRIAD task which modifies a visibility dataset by a model. It was derived from the task UVMODEL. Allowed operations are adding, subtracting, multiplying, dividing and replacing. The model is specified in the image domain, so that its Fourier transform is first computed before application to the visibilities. The model may be either an image (e.g., a CLEAN component image) or a point source.WSRT

An example is as follows. WSRTUVMODEL could be used to remove CLEAN components from a visibility data file. The residual data base could then be examined for anomalous points, which could in turn be clipped. WSRTUVMODEL could then be reapplied to add the CLEAN components back into the visibility data base for re-imaging.  


Input visibility data file. No default
Input model cube. The default is a point source model. This will generally be a deconvolved map, formed from the visibility data being modified. It should be made with ``channel'' linetype. The model should have units of JY/PIXEL and be weighted by the primary beam. The task DEMOS can be used to extract primary beam weighted models from a mosaiced image.
The standard uv selection subcommands. The default is all data.
This gives extra processing options. Several values can be given (though many values are mutually exclusive), separated by commas. Option values can be abbreviated to uniqueness. Possible options are (no default):
  add       Form: out = vis + model
  subtract  Form: out = vis - model
  multiply  Form: out = vis * model
  divide    Form: out = vis / model
  replace   Form: out = model
  flag      Form: out = vis, but flag data where the difference
            between vis and model is greater than "sigma" sigmas.
  unflag    Unflag any flagged data in the output.

  mosaic    This causes WSRTUVMODEL to select only those visibilities
            whose observing center is within plus or minus three
            pixels of the model reference pixel. This is needed
            if there are multiple pointings or multiple sources in
            the input uv file. By default no observing center
            selection is performed.
  mfs       This is used if there is a single plane in the input
            model, which is assumed to represen t the data at all
            frequencies. This should also be used if the model has
            been derived using MFCLEAN.
  zero      Use the value zero for the model if it cannot be
            calculated. This can be used to avoid flagging the
            data in the outer parts of the u-v-plane when subtracting
            a low resolution model.
The operations add, subtract, multiply, divide, replace and flag are mutually exclusive. The operations flag and unflag are also mutually exclusive.

The unflag option should be used with caution. Data in the output may still be flagged, if it was not possible to calculate the model.

Clip level. Pixels in the model below this level are set to zero. The default is not to perform any clipping.
If MODEL is blank, then the flux (Jy) of a point source model should be specified here. Also used as the default flux in the apriori option. The default is 1 (assuming the model parameter is not given). The flux can optionally be followed by i,q,u,v or the other polarisation mnemonics to indicate the polarisation type.
The RA and DEC offsets (arcseconds) of the point source from the observing center. A point source to the north and east has positive offsets. Defaults are zero.
The visibility linetype to use, in the standard form, viz:
Generally if there is an input model, this defaults to the linetype parameters used to construct the map. For a point source or planet model, the default is all channels. If you wish to override these defaults, or if the info is not present in the header, this parameter can be useful.
For options=flag, WSRTUVMODEL flags those points in the output that differ by more than "sigma" sigmas. The default is 100.
Output visibility data file name. No default. The output file will contain only as many channels as there are planes in the model cube. The various uv variables which describe the windows are adjusted accordingly.




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Time: 18:35:39 GMT, July 05, 2011